A number of LSI chips are used in electronic appliances currently distributed regardless of the types thereof.
Commonly, a LSI chip is once mounted on a wiring substrate for a package (hereinafter referred to also as an interposer), and the wiring substrate having the LSI chip mounted thereon, together with other parts, is mounted on a mother board (referred to also as a main board). This is because it may be technically and costly difficult to match the pitch of fine terminals (micro bumps 12) of the LSI chip with the pitch of terminals (solder balls 13) of the mother board that may be difficult to be made fine. With the progress of the technology node of the LSI chip, the pitch of the terminals has continued to be reduced, and the interposer that governs wiring relay with the mother board is also expected to be reduced in terminal pitch.
FIG. 1 illustrates one example of the configuration of the mother board mounting the wiring substrate including the LSI chip thereon. FIG. 2 illustrates one example of the detailed configuration of the wiring substrate.
Typically, a wiring substrate 11 has a structure in which one or more layers of a wiring layer 23 are formed on both surfaces of a core layer 21 composed of a predetermined core material, and the wiring layers formed on both surfaces are connected to each other via through holes 22 formed in the core layer 21.
As the core material constituting the core layer 21, an organic material such as glass epoxy, silicon, glass or the like is used, and the wiring substrates 11 using the organic material, the silicon and the glass are referred to as an organic substrate, a silicon substrate and a glass substrate, respectively.
Although the organic substrate has been used as the wiring substrate for years, the organic substrate has increasingly made it difficult to follow the miniaturization of the LSI. Accordingly, in recent years, attention is focused on the silicon substrate or the glass substrate allowing the wiring to be miniaturized.
These wiring substrates not only allow the wiring to be miniaturized, but also have high matching in thermal expansion coefficient with the silicon as a material of the LSI chip, making it possible to improve connection reliability. In particular, the glass substrate may have various advantages in satisfactory high frequency property caused by insulation of the glass, and the like over the organic substrate.
Meanwhile, the technical features applied to the silicon substrate or the glass substrate may include a through silicon via (TSV) and a through glass via (TGV). The TSV or TGV refers to a structure in which a through hole is formed in the core layer, and the formed through hole is filled with metal or the like to form a through electrode. Specifically, for example, a seed layer to be a current supply path is formed on a side face of the formed through hole, and plating is laterally grown within the through hole from the seed layer to fill the through hole with the plating to form the through electrode.
However, when the TSV or TGV is formed in the silicon substrate or the glass substrate, since an aspect ratio indicating a ratio of the depth to the diameter of the through hole is high and the absolute depth of the through hole is high, the plating filling after the opening of the through hole as described above may easily cause embedded failures (voids).
Accordingly, as one method to solve this problem, technology has been proposed in which a plating film is formed on one surface of the substrate to block one opening of the through hole, and plating is grown from the opposite surface in a semi-additive form by using the plating film as a current supply path to fill the through hole with the plating (see, for example, PTL 1).